Conventionally, in a case of scanning a moving site of the body using an X-ray CT (Computed Tomography) apparatus, artifacts caused by the movement are generated on an acquired tomographic image. In order to reduce the artifacts, generally, measurement is additionally performed for physiological movement during scanning using biological sensors such as an electrocardiograph and a respiratory sensor, and scanning is controlled using the acquired measurement signals to generate images.
For example, in a case of scanning the heart as a target, scanning is performed while electrocardiographic information is being measured using an electrocardiograph, and an appropriate cardiac phase is selected later in order to reconstruct a tomographic image in the selected cardiac phase (electrocardiographic synchronous reconstruction method).
As specific examples of the electrocardiographic synchronous reconstruction method, there are a method for performing image reconstruction by determining a scan data range that uses R-waves of an electrocardiographic waveform as a reference and a method for improving time resolution by collecting scan data in which cardiac phases are the same but the scan time is different and combining the collected scan data in order to perform image reconstruction. Although these methods can acquire image data of various cardiac phases using R-waves as a reference, an operator needs to select a diagnostically optimal image from a plurality of image data sets whose phases are different because it is desirable to diagnostically use a tomographic image in which the number of motion artifacts is the least.
On the other hand, there is a method for estimating the cardiac movement in order to automatically generate tomographic images of the heart in an arbitrary cardiac phase, in particular, a phase in which the cardiac movement is the smallest (static cardiac phase) by analyzing scan data or the tomographic images of the heart using the apparatus. For example, according to the method described in PTL 1 (Japanese Patent Publication No. 4157302), the cardiac movement is calculated by analyzing variation amounts of each data from scan data whose scan time is different and a plurality of tomographic images generated from the scan data.
Parameters typically analyzed include an integrated value of a CT value, a distance between feature points, a variation of the center of gravity, etc. Using these methods, an operator does not need to select a cardiac phase to be diagnostically used for an image because the apparatus performs data analysis to evaluate a static cardiac phase.